Why Does My Central Air Conditioner Keep Turning On and Off?

This is called “short cycling” and it can cost you big in energy bills and damage to your system’s compressor (a super expensive part to replace in an AC).

Here’s the kicker: There are a ton of different causes that trigger a system to short-cycle. That’s why we highly recommend calling a trusted professional to detect and fix this money-draining doozy.

If you want to understand the problem further and it’s common causes, read on.

We’ll discuss:

Why short cycling is bad for your system and your wallet

What causes it to happen

How the problem can be fixed

So, why is “short cycling” so bad?

In order to maintain your thermostat temperature setting, a healthy AC system naturally goes through an on/off cycle; it turns on, runs for an average 10 minutes or longer, then cycles off when temp is met.

Longer runtimes are typically better for your AC system because they are more efficient and help remove humidity from your home.

When your system is frequently turning on and off–we’re talkin’ every few seconds or minutes–that’s short cycling and it creates problems like:

Increased energy costs from constant system start-ups

Decreased life-span from excessive wear-and-tear

Costly repairs from over-worked equipment

Decreased comfort due to high humidity or temperature swings

What can cause an AC to short-cycle?

Like we said, there are a LOT of different causes surrounding this problem. Let’s break down some of the most common.

Bad thermostat location

Your thermostat tells your system when to cycle on and off based on the temperature around it. And poor placement can mess with your air conditioning system, causing short cycles.

For example, if your thermostat is located close to a vent, the cold blast of air coming from the vent can fool your thermostat into thinking your home is cool, shutting your system off. And when the air shuts off, your thermostat realizes your home is still warm and turns on your air conditioning system, repeating the cycle.

That’s why it should be located in a central area of your home, away from direct sunlight and any supply vents.

Dirty condenser unit/coils

Your outside condenser unit is made up of components that help dissipate heat from your home to the outside air.

If the unit looks dirty, chances are the condenser coils located inside are too. And the dirtier the condenser coils, the harder it is for these bad boys to do their job. This can trigger your system to work hard, overheat, shut off and repeat.

How it can be fixed:

Locate your outside condenser unit (the one with the fan)

Remove any visible leaves or debris

Wash the outside unit with a garden sprayer on a low setting (too high and you can damage some important parts in your AC)

Note: You’ll need a professional to properly clean your condenser coils, so let them do all the dirty work as part of an annual AC maintenance visit.

Frozen evaporator coil

Ice or frost forming on your evaporator coil (inside cooling coil) is a sign of restricted airflow and low pressure throughout your system.

Both of these issues can cause your system to freeze up. Then, when your system tries to cool your home, a safety device will quickly shut off your AC before it reaches its desired temp.

Important note: Frozen coils can lead to something called “liquid slugging”, which can destroy the compressor (that really expensive part we mentioned earlier). So make sure you don’t keep trying to run your system when it’s frozen!

Oversized AC

If short cycling has always been a problem since the day your system was installed, there is a good chance that the unit is too big for your home’s cooling needs. It cools your home quickly but doesn’t properly dehumidify your home’s air.

You likely also experience hot and cold spots in your home along with high energy bills.

How it can be fixed:The AC installation company probably didn’t do a proper Manual J calculation to determine the correct size air conditioner for your home. So you’ll need a trusted company to do this the right way. Learn more about improperly sized systems.

Other issues...

Whatever the cause, a short cycling AC system is BAD news all around. We recommend fixing this problem ASAP. As always, a trusted HVAC tech is the safest way for an effective and immediate solution.